DESCRIPTION: Paxillin is a 70 kDa protein localized to focal adhesions, points of attachment of the cell to the substratum. Tyrosine phosphorylation of paxillin and p125FAK, another focal adhesion protein, is stimulated by a number of different viral and cellular agents. Recent studies, performed by the applicant as a Postdoctoral Fellow, indicate that p125FAK and paxillin interact, and that pp125FAK can phosphorylate paxillin. The central hypothesis of the proposed research is that pp125FAK mediated tyrosine phosphorylation of paxillin regulates the formation of signaling complexes, by recruiting SH2 containing proteins. Four specific Aims are described. Sequences within pp125FAK and paxillin which mediate protein:protein interaction will be defined using the yeast two-hybrid method (Aim I). Next, the sites of Src and FAK-mediated phosphorylation on paxillin will be altered by mutating tyrosines to phenylalanines, and the ability of the mutated paxillin proteins to bind SH2 domains of known proteins will be assessed (Aim II). In Aim III, proteins that bind to paxillin, both known and unknown will be examined. Finally, the importance of paxillin containing signaling complexes will be determined by disrupting SH2-containing protein complexes bound to tyrosine phosphorylated paxillin. The effects on cell transformation and cell migration will be studied.